There has been known a device for detecting linear device values distributed in a matrix. Patent Literature 1, for example, discloses a touch sensor device (contact detecting device) for detecting distribution of capacitance values of a capacitance matrix Cij (i=1, . . . , M and j−1, . . . , L) formed between M drive lines and L sense lines. The touch sensor device operates in accordance with a scanning detection method; specifically, the touch sensor device sequentially selects one of the drive lines and thus detects respective values of linear devices connected to the drive line selected.
Patent Literature 2 discloses a capacitance detecting circuit which (i) in driving a plurality of drive lines, switches between a first drive line group and a second drive line group on the basis of a time series code sequence, (ii) outputs a measured voltage obtained by converting, into an electric signal, a sum total of respective currents across capacitances, connected to sense lines, at a plurality of intersections of driven drive lines with the sense lines, and (iii) performs a product-sum operation of such a measured voltage and the code sequence for each sense line so as to find a voltage value corresponding to a capacitance at each intersection.
Currently, introduction of a touch panel system into various kinds of electronic device including portable information devices such as smartphones and automatic vending machines such as automatic ticket vending machines is rapidly progressing.
In such electronic devices, there is a demand for a technique for preventing an incorrect operation caused by an unintended contact of an object with a touch panel.
For example, in a case where a user operates such an electronic device while carrying it in a user's hand, contact of the hand holding the electronic device with a touch panel is judged as a touch on the touch panel. Based on this judgment, an incorrect operation would occur in the electronic device. The incorrect operation caused by such a mechanism is expected to occur in a case where the electronic device is a portable apparatus such as a smartphone, a tablet-type terminal, notebook computer, or the like. This reduces convenience of a user.
FIG. 22 is a diagram explaining this mechanism. As illustrated in FIG. 22, when a hand (object) 73 holding a tablet-type terminal 71 makes contact with a touch panel 72 of the tablet-type terminal 71, the contact is judged as a touch on the touch panel 72. This reduces convenience of a user as mentioned above.
The problem of an incorrect operation caused by such a mechanism is expected to more frequently occur as a width of a frame with respect to a display screen in which a touch panel is provided becomes narrower.
Patent Literature 6 discloses a technique for preventing an incorrect operation of continuously detecting a specific coordinate position although no touch is made to a touch panel.
According to an input device disclosed in Patent Literature 6, in a case where detection of a specific coordinate position continues for a predetermined period of time, it is determined whether or not a difference between a detection value based on a change of an electrostatic field between electrodes and a reference value falls in a predetermined update detection range. In a case where the difference falls in the predetermined update detection range, the reference value is updated to the detection value. Note that the reference value is a value which serves as a standard by which presence or absence of a touch is judged based on the detection value. In a case where the detection value in a specific coordinate position is not less than the reference value or in a case where the detection value in a specific coordinate position is above the reference value, it is determined that a touch has been made to the coordinate position.
In this way, according to the input device disclosed in Patent Literature 6, it is possible to prevent an incorrect operation of continuously detecting a specific coordinate position although no touch is made to a touch panel. Moreover, sensitivity of detection may be improved by detecting presence or absence of a touch on the basis of the updated reference value.